Search

Byline: Konstantinos Nikolopoulos, Kostas S. Metaxiotis, Vassilis Assimakopoulos The major advantage of electronic markets over nonelectronic traditional market places is that trading partners use more sophisticated methods, rules and systems of information exchange. The internet has inevitably boosted this advantage over the last decade, making electronic markets the dominant 'playing field' for various industrial and business activities. Forecasting is one of them; it is important to firms because it can help ensure that resources are used effectively. In the market there are a number of off-the-self system products that provide forecasts. The new trend of moving traditional software packages to web services has pushed forecasting to a new dimension o e-forecasting, as called by the authors. In this paper we explore the challenges and opportunities arising from e-forecasting. Two very fertile e-areas for possible application are discussed in detail: e-government and forecasting community portals.

In this paper we address the adaptive and nonadaptive model reference control problem for a class of multivariable linear time-varying plants, namely index-invariant ones. We show that, under appropriate controllability and observability conditions, this class of plants admits a fractional description in terms of polynomial differential operators and, as such, allows for a polynomial equation-based controller design. We also show that, for a model reference control objective, the controller can be designed by solving a set of algebraic equations. Further, when the plant parameters are only partially known, we employ a gradient-based adaptive law with projection and normalization to update the controller parameters and establish the stability and tracking properties of adaptive closed-loop plant. Finally, we present a simple example to illustrate the design and realization of both the adaptive and nonadaptive control laws. Index Terms--Differential operators, Diophantine equations, model reference adaptive control, multivariable, time-varying systems.

The catalytic activity of supported silver nanoparticles on mesoporous silica was studied, for the selective reduction of azines into benzyl hydrazones using sodium borohydride as mild reducing agent. Different sizes of silver nanoparticles supported on mesoporous silica (Ag/HMS) were successfully prepared by two methods, i.e., wet impregnation followed by reduction with hydrogen at 350 °C and in situ deposition/reduction with a mixture of amines (ethanolamine and ethylenediamine). The Ag/HMS (amines) catalyst was found to promote the selective 1,2-reduction of aryl-substituted azines, compared to the corresponding 1,4-reduction that occurs in general reduction processes. This catalytic transfer hydrogenation process found to be clean, fast and quantitative (>99% yields and selectivity) towards benzyl hydrazone synthesis under mild conditions. Of great importance is that under the present catalytic conditions reducible functional groups remain intact. Formal kinetics, support the in situ formation of silver hydride species being responsible for the reduction process. The presence of protic polar methanol enhanced the catalytic activity of Ag/HMS. Based on the recycling studies the catalytic system Ag/HMS-NaBH4 was found to catalyze the selective reduction of azines nine times without significant loss of its activity. Finally, a one-pot reaction between the in situ produced benzyl hydrazones and a series of nitrostyrenes readily provided the regioselective synthesis of 1,3,5-subtituted pyrazoles, highlighting a useful synthetic application of the catalytic protocol. [ABSTRACT FROM AUTHOR]

Extrusion blown polyethylene and polyethylene/montmorillonite nanocomposite films were cold stretched to various ratios to quantify the influence of the crystal orientation and the nanofiller alignment on their dielectric breakdown performance. It was found that the crystal orientation could increase the breakdown strength (EBD) in the stretched blown films. The aligned pseudo-2D inorganic nanoclays provided additional strong improvements in EBD that can be superimposed to any EBD enhancement due to the polymer crystal orientation. At high filler loadings and high stretching ratios, the onset of percolation was observed through a substantial improvement in the dielectric breakdown strength. [ABSTRACT FROM AUTHOR]

Copyright of Sport-Orthopadie - Sport-Traumatologie is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Catalytic fast pyrolysis (CFP) of lignin with amorphous mesoporous aluminosilicates catalysts yields a high fraction of aromatics and a relatively low amount of char/coke. The relationship between the acidity and porosity of Al-MCM-41, Al-SBA-15, and Al-MSU-J with product selectivity during lignin CFP is determined. The acid sites (mild Brønsted and stronger Lewis) are able to catalyze pyrolysis intermediates towards fewer oxygenated phenols and aromatic hydrocarbons. A generalized correlation of the product selectivity and yield with the aluminum content and acidity of the mesoporous aluminosilicates is hard to establish. Zeolitic strong acid sites are not required to achieve high conversion and selectivity to aromatic hydrocarbon because nanosized MCM-41 produces a high liquid yield and selectivity. The two most essential parameters are diffusion, which is influenced by pore and grain size, and the active site, which may be mildly acidic, but is dominated by Lewis acid sites. Nanosized grains and mild acidity are essential ingredients for a good lignin CFP catalyst. [ABSTRACT FROM AUTHOR]

Isomerization of glucose to fructose is an important reaction with numerous applications in terms of biomass valorization. The reaction is catalyzed enzymatically but may also proceed under alkaline conditions, in which case it is accompanied by low selectivity and formation of byproducts. Solid Lewis acid and basic catalytic materials are being studied as alternative catalysts. In this work, the isomerization of glucose to fructose in aqueous media over homogeneous and heterogeneous catalysts has been investigated. The effect of polar aprotic solvents and their mixtures with water on glucose conversion and fructose selectivity was also studied. Sodium aluminate (NaAlO2) has been proven to be very effective, resulting in high fructose yield (52.1 %) and high selectivity (84.8 %). Among the various solid catalysts tested, MgO afforded glucose conversion of 44 %, with 75.8 % and 33.4 % fructose selectivity and yield, respectively, when the isomerization reaction was conducted in neat H2O. [ABSTRACT FROM AUTHOR]

Abstract: HDPE nanocomposites containing 0.5, 1, 2.5 and 5wt% of copper nanofibers (Cu-nanofibers) were prepared by the melt-mixing method and exhibited enhanced tensile strength, Young''s modulus, and oxygen barrier as well as antibacterial properties. These improvements were attributed to the small size of Cu-nanofibers and their fine dispersion into the HDPE matrix. [Copyright &y& Elsevier]

SUMMARY This paper discusses the use of H-infinity approximation for the online adaptation of PID controller parameters. For a frequency loop-shaping control objective, it is possible to adapt the PID parameters directly with linear model estimation algorithms. Standard least squares algorithms are common solutions for this problem, but their estimates exhibit a well-known strong dependence on the properties of the excitation. This drawback becomes more pronounced for systems where the modeling mismatch is large, as is frequently the case in PID control. In an alternative formulation of the estimation problem, we use a filter-bank to decompose the error signal to different components and minimize approximately the H-infinity norm of the sensitivity-weighted error operator. This approach results in a more consistent estimate of the optimal PID parameters, at the expense of higher excitation requirements. It also allows for the computation of a 'health indicator' to describe the confidence in the estimated parameters. The practical implication of this observation is that PIDs can be tuned more reliably, even in cases of large mismatch between the target and the feasible loop shapes. It also suggests a general theme where a min-max optimization of an operator error provides an advantage over signal error optimization. The key aspects of the algorithm are illustrated by numerical examples. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The natural resistance to enzymatic deconstruction exhibited by lignocellulosic materials has designated pretreatment as a key step in the biological conversion of biomass to ethanol. Hydrothermal pretreatment in pure water represents a challenging approach because it is a method with low operational costs and does not involve the use of organic solvents, difficult to handle chemicals, and 'external' liquid or solid catalysts. In the present work, a systematic study has been performed to optimize the hydrothermal treatment of lignocellulosic biomass (beech wood) with the aim of maximizing the enzymatic digestibility of cellulose in the treated solids and obtaining a liquid side product that could also be utilized for the production of ethanol or valuable chemicals. Hydrothermal treatment experiments were conducted in a batch-mode, high-pressure reactor under autogeneous pressure at varying temperature (130-220 °C) and time (15-180 min) regimes, and at a liquid-to-solid ratio (LSR) of 15. The intensification of the process was expressed by the severity factor, log Ro. The major changes induced in the solid biomass were the dissolution/removal of hemicellulose to the process liquid and the partial removal and relocation of lignin on the external surface of biomass particles in the form of recondensed droplets. The above structural changes led to a 2.5-fold increase in surface area and total pore volume of the pretreated biomass solids. The enzymatic hydrolysis of cellulose to glucose increased from less than 7 wt % for the parent biomass to as high as 70 wt % for the treated solids. Maximum xylan recovery (60 wt %) in the hydrothermal process liquid was observed at about 80 wt % hemicellulose removal; this was accomplished by moderate treatment severities (log Ro=3.8-4.1). At higher severities (log Ro=4.7), xylose degradation products, mainly furfural and formic acid, were the predominant chemicals formed. [ABSTRACT FROM AUTHOR]

In this work we provide evidence of microporosity in the nanostructured mesoporous aluminosilicates MSU-S/W(BEA) synthesized from zeolite BEA seeds, based on the so called I-point plots (refs. 18–20) of the BET equation. Seventeen solids were characterized for their porous characteristics as follows: (i) one mesoporous aluminosilicate 2%Al-MSU-S/W(BEA), (ii) two typical mesoporous MCM-41 materials, one pure silica and one aluminosilicate 2%Al-MCM-41, (iii) three typical microporous zeolites, i.e., zeolites Y, ZSM-5 and beta, (iv) two typical amorphous silica–alumina (ASA) samples, (v) five mechanical mixtures of mesoporous Al-MCM-41 with zeolite beta at different addition percentages, and (vi) four amorphous or partially crystalline ZSM-5 based aluminosilicates. The P,V data from the nitrogen-adsorption isotherms of those porous solids were plotted according to the I-point modification of the BET equation in the form V[1 − (P/P0)]/(P/P0) = CVm− (C− 1)V[1 − (P/P0)]. Plots of V[1 − (P/P0)]/(P/P0) vs. V[1 − (P/P0)] provided lines which have the shape of an inclined V, i.e. >, and variable slopes corresponding to (C− 1) from which the values of the C parameter were determined for the whole range of partial pressures 0 < P/P0 < 1. The inversion point of the above plots, called the I-point, projected onto the V[1 − (P/P0)] axis corresponds exactly to the volume of the monolayer Vm = VI[1 − (PI/P0)], from which the value of the specific surface area SI (m2 g−1) was determined. The shape of the I-plots depended strongly on the type of porous solids, i.e. microporous/zeolitic and partially crystalline zeolitic materials with combined micro- and meso/macroporosity; ordered mesoporous MCM-type materials; ASA materials with random mesoporosity; and mechanical mixtures of zeolite beta with MCM-41. The I-plot for the MSU-S/W(BEA) solid exhibited the combined characteristics of the plots of ordered mesoporous MCM-41 samples and of partially crystalline zeolitic materials, thus proving the presence of microporous domains within the homogeneous mesoporous structure of the MSU-S material. The I-plot result supports the proposed presence of protozeolitic subunits in the framework walls, of MSU-S, even though XRD and electron diffraction TEM studies have shown the material to be free of any zeolitic crystalline phase. The surface areas estimated by the I-method were similar to those provided by the BET model for the zeolitic and the ASA samples, while in the case of the ordered MCM-41 and MSU-S/W(BEA) mesostructures, two surface area values can be estimated based on different interpretations of the I-method, one similar to the value from the BET model and one supported by the modified CPSM model (refs. 31–34). [ABSTRACT FROM AUTHOR]

The effects of rootstock variety (41B, 1103P and 110R), irrigation level (0.50, 0.75 and 1.00 of the evapotranspiration) and water quality (recycled versus freshwater) on water relations and gas exchange of potted Soultanina grapevines were investigated during two growing seasons. An early reduction of predawn leaf water potential (Ψpd) was detected for vines irrigated with recycled water in both the seasons. However, assimilation rate (A) and stomatal conductance (gs) were reduced only late in the first year at higher irrigation levels. This was consistent with the higher reduction of Ψpd at these treatments indicating that the development of a water deficit due to salt accumulation reduced gas exchange. At midday during 1998, leaves on vines grafted on 1103P and 110R had lower leaf water potentials and higher gs and A. An opposite effect was however observed early in June the following season, although later in that season no differences were detected among rootstocks. That differentiation of rootstock effect between seasons may have been induced by alterations in source/sink relations due to differences in yield among rootstocks and its effects on leaf area. Irrigation level strongly affected water relations and gas exchange. Both A and gs were significantly correlated with soil moisture. A differentiation in these relations was observed among rootstocks late in 1998 which probably resulted from the change in leaf area development among rootstocks during that period. [Copyright &y& Elsevier]